1. Field of the Invention
The present invention concerns a fan with an integrated fan motor including a revolving fan impeller with a fan blade ring and a turbine blade ring. This latter element may be impinged upon by a pressurized fluid and is used to drive the impeller.
2. Description of the Related Art
Fans of this type are used for various purposes, including providing ventilation in rooms or areas, removing stagnant air, and producing low pressure in technical equipment. Fans of this type are known from DE 200 12 843 (File PN 11144).
For example, low pressure is required in a vacuum belt conveyor arrangement. Vacuum belt conveyor arrangements are used to facilitate the threading of a paper web, specifically in a machine used to produce or convert or further process a web of this type. In the course of starting up a paper machine (or restarting the machine following a break in the web), a small narrow ribbon or lead-in strip is separated from the moving web. One example application of the vacuum belt conveyor arrangement is to help transfer this ribbon from the end of one machine section to the intake zone of a subsequent machine section.
In principle, the fan known from aforementioned DE 200 12 843 is adequately suited to the task of producing low pressure in a vacuum belt conveyor arrangement. Its suitability for this purpose is based on the fact that the fan is designed to be extremely compact, enabling it to be placed within the loop of the endless conveyor belt of the vacuum belt conveyor arrangement. However, one drawback lies in the fact that the drive power of the turbine blade ring may only be adjusted to a desired setting through varying the pressure of the pressurized fluid. This is associated with the fact that the feed channel (positioned in the casing), through which the pressurized fluid is directed to the turbine blade ring, is left fully open the entire time. This results in a further disadvantage, inasmuch as the quantity of pressurized fluid flowing through the turbine blade ring remains relatively high, even if the pressurized fluid is set at a relatively low pressure.
The present invention provides a design of an improved fan of the aforementioned known type, wherein the driving power of the turbine blade ring may be varied more satisfactorily than in previous designs, and where the level of power required at any specific point in time may be attained with the smallest possible quantity of pressurized fluid.
This goal is accomplished, according to the present invention, by arranging a certain number of nozzles, through which the pressurized fluid flows, between the pressurized fluid feed channel and the turbine blade ring as already known from U.S. Pat. No. 3,904,324 or U.S. Pat. No. 5,275,533. Furthermore, the present invention incorporates the hitherto unknown measure of providing for a variable number of active nozzles. In other words, at any given point in time, a greater or smaller number of nozzles will be connected with the feed channel, depending on the power required for the turbine blade ring. In cases where relatively low power is required for the turbine blade ring, this means that only a relatively small number of nozzles (perhaps even just one nozzle) shall be used for impinging the pressurized fluid on the turbine blade ring. This considerably reduces the amount of pressurized fluid consumed. It therefore becomes unnecessary to vary the pressure of the fluid, except in cases where fine-tuning of the required power is desired. In a further embodiment of the present invention, the nozzles may be positioned together in a nozzle group, extending over just one section of the turbine blade ring. Using this method, only a relatively short feed channel is required within the fan casing for the pressurized fluid.
In accordance with an additional and preferred embodiment of the present invention, the number of active nozzles is varied through shifting the position of the nozzles in relation to the feed channel. Where necessary, the nozzles may be shifted during operation or during a stop period. In many cases, however, all that is required is to set the number of active nozzles at the moment when the fan is being assembled. This option is recommended in cases where it is anticipated that the power of the turbine blade ring (and thus desired fan performance, i.e. the level of low pressure produced) will remain unchanged over a significant period of time. This would apply, for example, in a situation where the fan was to be used in the vacuum belt conveyor arrangement of a papermaking machine, which had been selected to manufacture the same type of paper over a relatively long period of time. If it should become necessary at a later time to alter the power of the turbine blade ring, the fan according to the present invention may be quickly and easily adjusted, so as to change the number of active nozzles.